1. Field of the Invention
The present invention relates to an alternator equipped with a rectifier for rectifying alternating current generated at a stator coil into direct current.
2. Description of the Related Art
FIG. 10 is a sectional view of a conventional automotive alternator, FIG. 11 is an electrical circuit diagram of the alternator, FIG. 12 is a front view of a rectifier 12 of FIG. 10 when the rectifier 12 is observed from inside, and FIG. 13 is a front view of a rear bracket 2 of FIG. 10.
The automotive alternator includes: a case 3 composed of an aluminum front bracket 1 and an aluminum rear bracket 2; a shaft 6 rotatably disposed in the case 3 and which has a pulley 4 secured to one end thereof; a Lundell-type rotor 7 secured to the shaft 6; a stator 8 secured to an inner wall of the case 3; a slip ring 9 secured to the other end of the shaft 6 and which supplies electric current to the rotor 7; a pair of brushes 10 that slide in contact with the slip ring 9; a brush holder 11 accommodating the brushes 10; a rectifier 12 electrically connected to the stator 8 and which rectifies alternating current generated in the stator 8 into direct current; a heat sink 17 fitted in the brush holder 11; and a regulator 18 adhesively fastened to the heat sink 17 and which adjusts an alternating voltage generated in the stator 8.
The rotor 7 is equipped with a rotor coil 13 for generating magnetic flux on passage of electric current, and a pole core 14 covering the rotor coil 13 in which magnetic poles are produced by the magnetic flux. The pole core 14 has a pair of a first pole core assembly 21 and a second pole core assembly 22 that intermesh with each other. Centrifugal fans 5 for cooling are welded on axial end surfaces of the first pole core assembly 21 and the second pole core assembly 22.
The stator 8 is provided with a stator core 15 through which a rotating magnetic field generated by the rotor 7 passes, and a stator coil 16 in which alternating current is generated by the rotating magnetic field. The stator coil 16 is constructed by a first stator coil section 16a and a second stator coil section 16b, each being formed of three coils whose conductors are wound around the stator core 15 and which are in Y-connection.
FIG. 14 is a front view of the rectifier 12, and FIGS. 15 and 16 are exploded front views of the rectifier 12 of FIG. 14. The rectifier 12 includes positive-side diodes 26 and negative-side diodes 28 connected to output ends of the first stator coil section 16a and the second stator coil section 16b, and neutral point diodes 30 connected to neutral points 31 of the first stator coil section 16a and the second stator coil section 16b. 
The rectifier 12 further includes: a circular strip-shaped positive-side heat sink 24 having, on its surface, six positive-side diodes 26 and two neutral point diodes 30 equidistantly provided on the same circumference; a circular strip-shaped negative-side heat sink 27 disposed radially outside of and on the same plane as the positive-side diodes 26, and has, on its surface, six negative-side diodes 28 and two neutral point diodes 30 equidistantly provided on the same circumference; and a circuit board 29 electrically connecting the diodes 26, 28, and 30, and the stator coil 16.
The surfaces of the positive-side heat sink 24 and the negative-side heat sink 27 have recesses 32 and 33 for accommodating the columnar positive-side diodes 26, the negative-side diodes 28, and the neutral point diodes 30. FIG. 17 shows the positive-side heat sink 24 and the negative-side heat sink 27 of the FIG. 15 as observed from a rear side. On the rear surfaces of the heat sinks 24 and 27, protuberances 34 and 35 are formed at the same time when the recesses 32 and 33 are formed.
The positive-side diodes 26, the negative-side diodes 28, and the neutral point diodes 30 are fixed to the recesses 32 and 33 of the heat sinks 24 and 27 by soldering. Perpendicularly extending lead wires 36 and 37 of the diodes 26, 28, and 30 are electrically connected to terminals 38 and 39 of the circuit board 29.
The positive-side heat sink 24 is retained on the negative-side heat sink 27 via a holder 40. The positive-side heat sink 24, the negative-side heat sink 27, and the circuit board 29 are fixed in the case 3 by screws (not shown) attached to the rear bracket 2 via through holes 41. Furthermore, the negative-side heat sink 27 is grounded by being directly attached to the rear bracket 2.
In the automotive alternator having the construction set forth above, electric current is supplied from a battery (not shown) to the rotor coil 13 via the brushes 10 and the slip ring 9, generating magnetic flux. The pulley 4 is driven by an engine, and the rotor 7 is rotated by the shaft 6. This causes a rotating magnetic field to be imparted to the stator coil 16, so that an electromotive force is generated in the stator coil 16. The alternating electromotive force is converted into direct current through the positive-side diodes 26 and the negative-side diodes 28 of the rectifier 12, a magnitude thereof is adjusted by the regulator 18, and the battery is recharged.
The rotor coil 13, the stator coil 16, the positive-side diodes 26, the negative-side diodes 28, and the regulator 18 constantly generate heat during power generation. When an alternator of, for example, a 100 A rated output current class, runs at a speed generating a high temperature, the rotor coil 13 generates a calorific value of 60 W, the stator coil 16 generates a caloric value of 500 W, the positive-side diodes 26 and the negative-side diodes 28 together generate a calorific value of 120 W, and the regulator 18 generates a calorific value of 6 W. Excessive heat generation causes deteriorated performance of the alternator and shortens lives of components.
As countermeasures for the heat generation, the fans 5 rotate as the rotor 7 rotates. The rotation of the fans 5 causes outside air to be introduced into the case 3 through an aperture A of the case 3, and to flow as indicated by arrows xcex1 of FIG. 10 to thereby cool the negative-side heat sink 26, the negative-side diodes 28, the positive-side heat sink 24, and the positive-side diodes 26. The outside air is then led radially outward by the fans 5 to cool a coil end of the stator coil 16 at the rear side, and exhausted to open air through an aperture B.
Furthermore, the rotation of the fans 5 causes outside air to be introduced into the case 3 also through an aperture C. The outside air flows as indicated by arrows xcex2 of FIG. 10 to cool a power transistor of the regulator 18. The outside air is then led radially outward by the fans 5 to cool a coil end of the stator coil 16 at the rear side, and exhausted to open air through an aperture D.
Similarly, outside air introduced through apertures E of the front bracket 1 is directed radially outward by the fans 5 to cool an end of the stator coil 16 at a front side. The outside air is then exhausted out of the case 3 through an aperture F.
In the automotive alternator having the construction described above, the lead wires 36 and 37 of the positive-side diodes 26 and the negative-side diodes 28, which extend in an axial direction of the shaft 6, are directly abutted against the terminals 38 and 39 of the circuit board 29. For this reason, the six positive-side diodes 26 and the two neutral point diodes 30 are disposed at equal intervals on the circumference of the positive-side heat sink 24, and the six negative-side diodes 28 and the two neutral point diodes 30 are disposed at equal intervals on the circumference of the negative-side heat sink 27. Therefore, the positive-side diodes 26, in particular, on the positive-side heat sink 24 on an inside diameter side are close to each other. When a distance between central points of the positive-side diodes 26 is denoted as W, and a diameter of the positive-side diodes 26 is denoted as D, a value expressed as W/D≅1.5 is obtained. A study of temperature distribution of the rectifier 12 has revealed that the temperature rises toward a center in a circumferential direction of the positive-side heat sink 24, a difference between temperature extremes being approximately 13 degrees Celsius, while the temperature rises inward in a radial direction, a difference between temperature extremes being approximately 3 degrees Celsius. There has been a problem in that the positive-side diode 26 at the center of the positive-side heat sink 24 where the temperature is the highest reaches a locally high temperature, 125 degrees Celsius.
Accordingly, the present invention has been made with a view toward solving the problems described above, and it is an object thereof to provide an alternator that exhibits uniform temperature distribution in a rectifier, thereby preventing a locally hot place from being developed.
To this end, according to one aspect of the present invention, there is provided an alternator having at least a first diode assembly or a second diode assembly composed of diodes on an inside diameter side and diodes on an outside diameter side arranged in a zigzag pattern in a circumferential direction.
In a preferred form of the alternator in accordance with the present invention, the diodes on the inside diameter side and the diodes on the outside diameter side are provided in recessions of a heat sink having a recessed surface, and protuberances associated with the recesses are formed in a rear surface of the heat sink.
In a preferred form of the alternator in accordance with the present invention, one of the diode on the inside diameter side and the diode on the outside diameter side is disposed such that it is partly included in a region of an air detachment portion produced on a peripheral surface by cooling air that collides with the other of the diode on the inside diameter side and the diode on the outside diameter side.
In another preferred form of the alternator in accordance with the present invention, if a distance between a central point of a columnar diode on the inside diameter side and a central point of its adjacent columnar diode on the outside diameter side is denoted as W, and a diameter of the diode on the inside diameter side and the diode on the outside diameter side is denoted as D, then (W/D) less than 2. Furthermore, if an angle at which a line connecting a central point of the diode on the inside diameter side and a central point of its adjacent diode on the outside diameter side crosses a line connecting a central axis of a shaft and the central point of the diode on the outside diameter side or the diode on the inside diameter side is denoted as xcex8, then angle xcex8 is 100xc2x0 less than xcex8 less than 140xc2x0.
In a preferred form of the alternator according to the present invention, diodes on the outside diameter side that are secured to the second heat sink are disposed so as to oppose the diodes on the outside diameter side that are secured to the first heat sink.
In a preferred form of the alternator according to the present invention, the diodes on the outside diameter side and the diodes on the inside diameter side that are secured to the second heat sink are disposed away from radial lines of the diodes on the outside diameter side and the diodes on the inside diameter side that are secured to the first heat sink.
In a preferred form of the alternator according to the present invention, the first heat sink and the second heat sink are disposed on different vertical planes with respect to axes.
In a preferred form of the alternator according to the present invention, the first heat sink is a positive-side heat sink, the first diode assembly is a positive-side diode assembly, the second heat sink abutted against the case is a negative-side heat sink, and the second diode assembly is a negative-side diode assembly.